The production of carbon black under controlled conditions has become increasingly important in recent years. The more constant the individual parameters of the carbon black process are kept, the more reliable and predictable the carbon black properties will be. Unfortunately, a variety of carbon black process parameter variations occur which are not readily controllable economically. One of the most significant of such parameter variations is the water content of the free oxygen-containing gas such as air used during the fuel combustion for heating the carbon black feedstock to carbon black forming temperature. The water content of the air, which can also be expressed as the relative humidity of the air at a given temperature, has a significant influence on such important carbon black process parameters as conversion, production rate, iodine number, etc. Although it is possible to operate a carbon black plant with air of controlled water content, the required pretreatment of the air or the other free oxygen-containing gas utilized is frequently economically prohibitive.
It has been proposed in the prior art to control the quality of the carbon black by manipulating the hydrocarbon feed rate responsive to the water content in the free oxygen-containing gas stream. Whereas this proposal has been a significant contribution to the carbon black art, it would be desirable to have available a more flexible control system that allows further optimization of the carbon black process without sacrificing quality control of the carbon black produced.